The present invention relates to a method of producing packages provided with an opening arrangement and of the type which has an emptying hole prepared in the package wall and through which the package is intended to be emptied of its contents, the method comprising the steps of coating one side of a web of paper or paperboard with a liquid-tight coating, of plastic, and the other side with a foil or coating of metal which serves as oxygen gas barrier and which, by means of a layer of sealing plastic or other suitable adhesive, is bonded to the paper or paperboard web; of making emptying-preparatory holes in the thus coated paper or paperboard web and thereafter reforming the packaging blank provided with the hole into individual packages provided with an opening arrangement.
Within the packaging industry, use is now often made of packages of single-use disposable type for the transport and handling of liquid foods, and a very large group of these so-called single-use disposable packages is produced from a packaging laminate which comprises a paper or paperboard layer and liquid-tight coatings of plastic on both sides of the paper or paperboard layer. Examples of commercial packages of this type are TETRA BRIK(copyright) and TETRA REX(copyright).
For foods which have a relatively rapid turnover in retail outlets and, as a result, relatively short shelf-life in their package, a packaging laminate solely of paper or paperboard and outer liquid-tight coatings of plastic is often sufficient to impart to the packed food the requisite product protection throughout its entire storage life from filling to consumption. On the other hand, for more perishable and storage-sensitive foods which are intended to be able to be stored for a relatively lengthy period of time in their packages, it is necessary that the packaging laminate be supplemented with at least one additional layer in order to make for extended shelf-life. In particular, it is necessary that the package be sufficiently tight in order, during the entire storage life of the packed food in its unopened package, to prevent the penetration of oxygen gas which could very rapidly cause deterioration in the food if it came into contact with the food.
In order to make for the packing of such perishable, storage- and oxygen gas-sensitive foods with extended shelf life, the packaging laminate is therefore normally supplemented with at least one additional layer of metal or plastic of other type than that employed in the outer plastic coatings of the packaging laminate. The most common packaging laminate for this purpose includes, as the above-mentioned additional layer, an aluminum foil which is practically entirely impermeable to oxygen gas and which, moreover, possesses the advantageous property that it makes possible inductive thermosealing which is a simple, but efficient method of rapidly obtaining mechanically strong and tight sealing joints or seams when the sheet- or web-shaped packaging blank is reformed during the package production operation.
In addition to the requisite mechanical and physical properties so as to make for lengthy storage of foods with good shelf life, it is also desirable from the point of view of the consumer that the package can be easy to open when it is time to empty the package of its contents. In order to satisfy this need and provide a conveniently openable package, the package is therefore provided with some type of arrangement which facilitates opening and which may either be integral in or be a separate part of the package.
An extremely well-known and well-functioning opening arrangement includes an emptying hole prepared in the paper or paperboard layer of the package wall and which is closed from inside and outside by respective surrounding layers in the package wall. In order to facilitate exposure of the emptying hole when the package is to be opened, the opening arrangement normally includes a separate opening strip fixedly secured on the outside of the package wall and whose removal entails that the subjacent part of the package wall is entrained and torn off along the incision edges of the hole so that the entire hole is exposed.
Other types of exteriorly applied opening arrangements for facilitating exposure of an emptying hole prepared in the package wall are also known in the art, but since they do not constitute a germane part of the present invention, they need not be described in greater detail here in order to understand the present invention.
A packaging blank for a packaging container of the type described by way of introduction is produced, according to a conventional method, from a rolled web of paper or paperboard. The rolled web is unwound from the reel and is led through a printing station where the web is provided with the desired decorative artwork and possibly other printing markings relevant for subsequent web operations. The printed web is thereafter led further to a mechanical processing station where the web, in a per se known manner, is given the desired pattern of crease lines and also provided with through-going holes of the desired size and configuration which correspond with the emptying opening of the finished package. From the processing station, the web is thereafter led further to a coating station where the web is coated on both its sides with liquid-tight plastic coatings, and possibly additional layers necessary for the packaging purpose, e.g. an aluminum foil (Alifoil) in that case when the web is later to be used for the production of packages for, for instance, oxygen gas-sensitive products. Finally, from the coating station, the web is wound up on package magazine reels for storage or further transport to a packing machine where the web is supplemented with separate opening details in the areas of the prepared emptying hole, and is thereafter formed, filled and sealed to form individual consumer packages provided with an opening arrangement.
Packages produced according to this conventional method generally function well in those cases when the packaging laminate merely consists of paper or paperboard and outer coatings of plastic, while corresponding packages in which the packaging laminate also includes an aluminum foil show a tendency to lose tightness properties against oxygen gas or right from the outset display deteriorating tightness properties against oxygen gas, in particular within the area of the emptying hole prepared in the package wall. While the packages in most cases maintain sufficient oxygen gas tightness to impart to the packed product satisfactory protection during at least a major part of the storage life of the product in the unopened package, it is naturally a need in the art to be able to produce packages which right from the outset display a high level of oxygen gas tightness which, moreover, is maintained during the remaining part of the storage life of the product in its package.
According to another conventional method, packaging containers provided with an opening arrangement are produced from a similar packaging blank to that described above, but which, unlike the previous packaging blank, is not provided with any through-going emptying hole before the coating with the additional layer of plastic and aluminum. In this case, the emptying-preparatory holes are made on the ready-coated packaging blank by means of punching tools in connection with the packing and filling machine, where after the thus provided holes are closed with the aid of an applicator which applies a sealing plastic patch or strip over the hole before the packaging blank is led in and reformed into packages in the packing and filling machine.
Packages produced according to this conventional method function well also in that case when the packaging laminate includes an aluminum foil, and such packages are moreover conveniently openable, but one serious drawback is that the method requires extremely accurate register maintenance and therefore complicated technical equipment in order to place the emptying holes in the correct position in relation to the printed artwork and crease line pattern of the packaging blank and in order to apply the sealing plastic patch or plastic strip in such a manner that it impenetrably but tightly seals the hole provided in the package wall.
One object of the present invention is therefore to provide an indication of how the above-described shortcomings and drawbacks inherent in the prior art technology may be obviated or at least considerably reduced.
A further object of the present invention is to provide a method of producing packaging containers, provided with an opening arrangement, of the type described by way of introduction which, unlike the prior art packaging containers, right from the outset display an oxygen gas tightness which is sufficiently high and stable so as to make possible long-term storage of a perishable, storage- and oxygen gas-sensitive product with good shelf life.
Yet a further object of the present invention is to provide a method of producing packaging containers, provided with an opening arrangement, with increased flexibility for an individual manufacturer of packages.
These objects are attained according to the present invention by the method as defined in appended claim 1.
One key difference between the method according to the present invention and the former method as described above is, thus, that the provision of the emptying hole in the method according to the present invention is to take place on the ready-produced packaging blank, and hence not only on the paper or paperboard web in connection with the production of the packaging blank, as in the prior art conventional method.
One key difference between the method according to the present invention and the second conventional method as described above is further that the emptying holes, in the method according to the present invention, are made only partly through the packaging blank, i.e. from the one side of the packaging blank through the outer plastic coating and the paper or paperboard layer down to, but not through, the subjacent aluminum foil which, thus, together with the outer plastic coating on the other side of the packaging blank, remain unpenetrated or intact on the packaging blank.
As a result of this unique partial hole provision on the finished packaging blank, inter alia the advantage will be afforded that the unruptured or intact aluminum foil (which is nevertheless already present in the packaging blank) can effectively be utilized for oxygen gas-tight closure of the emptying hole which, granted, can but need not be closed separately with an extra plastic strip or plastic patch as in the prior art method.
The deteriorated oxygen gas-tightness in prior art packages provided with opening arrangements of the above-described type, in particular in the region of the emptying opening prepared in the package wall is because of the fact that it has been difficult for process-related reasons, to achieve a strong internal bonding of the individual layers included in the packaging laminate, i.e. the aluminum foil and the plastic, within this region. When the paper or paperboard web with holes provided is coated with aluminum foil and plastic, and is, in connection with, or immediately after such coating led through the nip between a press roller and a counter-pressure roller in order, under pressure, to compress and bond the layers to one another, the necessary compression pressure against the web is attained only in those web areas which are not hole-punched, i.e. where the web is wholly continuous, while but a lower (insufficient) pressure is attained in remaining areas of the web, i.e. in the regions of the punched holes.
On the other hand, in the method according to the present invention, where the paper or paperboard web lacks the provision of holes, the same requisite pressure can be attained transversely across the entire web and within all regions of the web.
The partial provision of the emptying-preparatory holes in the well-integrated packaging web according to the present invention may be put into effect mechanically with the aid of punching tools which, at selected points, punch or cut incision lines of the same size and configuration as the desired emptying opening down to a pre-set depth in the packaging web, e.g. down to the aluminum foil beneath the paper or paperboard layer, where after the web portions defined by the incision lines (so-called confetti) are removed from the web for the formation of partly provided emptying holes on the upper side of the packaging web.
According to the present invention, the partly provided emptying holes are preferably realized with the aid of laser equipment which directs a cutting laser beam along a line corresponding to the opening configuration of the emptying opening down to the desired depth in the packaging material, i.e. through the plastic coating, and the paper or paperboard layer down to the subjacent aluminum foil, from the one side of the packaging web. The advantage in laser cutting as compared with mechanical punching is that laser cutting is mechanically contactless with the moving packaging web and therefore does not involve any moving mechanical components which are worn as a result of physical contact with the moving packaging web or with any other moving machine part. A further major advantage is that a laser beam is easy to direct and set to the desired cutting depth during ongoing processing, without the need to stop the packaging web or otherwise arrest operation.
The parts of the packaging web defined by the incision lines are thereafter removed in a conventional manner by means of vacuum which sucks or draws off these from the packaging web and leaves the partly through-going holes in the packaging web.
In order to facilitate this removal by suction or drawing of the confetti from the packaging web, heat is applied to the web simultaneously within the pertinent confetti regions, whereby the sealing plastic or adhesive between the paper or paperboard layer and the aluminum foil is melted and, as a result, the confetti may more easily release is grip on the subjacent aluminum foil.
Preferably, the packaging web is heated within the selected regions by induction heating which is an efficient and reliable heating method also at extremely high web speeds.
The partly through-going emptying holes in the packaging web can thereafter be sealed with separate opening strips which are fixedly sealed on the one side of the packaging web in a mechanically strong, but rupturable sealing joint around the entire opening contour of the hole. Alternatively, or in addition, the exposed fiber incision edges may be impregnated or covered with a water-repellent coating prior to the application of the opening strips.
According to the present invention, it is further possible, possibly after a preceding impregnation of the exposed fiber incision edges within the regions of the provided emptying holes, to form, fill and seal packages from the hole-provided packaging web and thereafter apply separate, e.g. injection moulded arrangements above each respective emptying hole on each individual package in connection with the package""s departing from the packing and filling machine. Such opening arrangements are known to persons skilled in the art and occur in a multiplicity of different variations and, therefore, need not be described in greater detail in this context.